Working Papers

Abstract: Trading networks generalize and unify models of matching with bilateral contracts and indivisible goods exchange. We extend earlier models' canonical definitions of substitutability to the trading network context and show that all these definitions are equivalent. We also find that substitutability is preserved under economically important transformations such as mergers, limited liability, and trade endowments. Furthermore, we show that substitutability implies a regularity condition called the Laws of Aggregate Supply and Demand.

Abstract: We show that in trading networks with bilateral contracts, a suitably adapted notion of chain stability (Ostrovsky, 2008) is equivalent to stability (Hatfield et al. 2013) if all agents' preferences are fully substitutable.

(joint with Alexey Kushnir)University of Zurich, Working Paper Series, April 2014.

Abstract: We introduce a simple two-stage game of endogenous network formation and information sharing for reasoning about the optimal design of social networks like Facebook or Google+. We distinguish between unilateral and bilateral connections and between targeted and collective information sharing. Agents value being connected to other agents and sharing and receiving information. We consider multiple utility specifications. We show that the game always has an equilibrium in pure strategies and then we study how the network design and the utility specifications affect welfare. Surprisingly, we find that in general, targeted information sharing is not necessarily better than collective information sharing. However, if all agents are either "babblers" or "friends", irrespective of whether the network is unilateral or bilateral, in equilibrium, targeted information sharing yields higher welfare than collective information sharing.

Abstract: In models of matching in networks, when transfers are not allowed or are only allowed to be discrete, both substitutability of preferences and supply chain structure of the contractual set are required for the guaranteed existence of stable outcomes. We show that when continuous transfers are allowed and utility is quasilinear, the substitutability of preferences is on its own both sufficient and necessary for the guaranteed existence of stable outcomes. Furthermore, when preferences are substitutable, the set of stable outcomes is equivalent to the set of competitive equilibria, and all stable allocations are efficient.

Abstract: The evaluation of scientific output has a key role in the allocation of research funds and academic positions. Decisions are often based on quality indicators for academic journals and over the years a handful of scoring methods have been proposed for this purpose. Discussing the most prominent methods (de facto standards) we show that they do not distinguish quality from quantity at article level. The systematic bias we find is analytically tractable and implies that the methods are manipulable. We introduce modified methods that correct for this bias, and use them to provide rankings of economic journals. Our methodology is transparent; our results are replicable.

Abstract: One-sided assignment problems combine important features of two well-known matching models. First, as in roommate problems, any two agents can be matched and second, as in two-sided assignment problems, the division of payoffs to agents is flexible as part of the solution. We take a similar approach to one-sided assignment problems as Sasaki (Int J Game Theory 24:373–397, 1995) for two-sided assignment problems, and we analyze various desirable properties of solutions including consistency and weak pairwise-monotonicity. We show that for the class of solvable one-sided assignment problems (i.e., the subset of one-sided assignment problems with a non-empty core), if a subsolution of the core satisfies [Pareto indifference and consistency] or [invariance with respect to unmatching dummy pairs, continuity, and consistency], then it coincides with the core (Theorems 1 and 2). However, we also prove that on the class of all one-sided assignment problems (solvable or not), no solution satisfies consistency and coincides with the core whenever the core is non-empty (Theorem 4). Finally, we comment on the difficulty in obtaining further positive results for the class of solvable one-sided assignment problems in line with Sasaki's (1995) characterizations of the core for two-sided assignment problems.